Approximately
1 in 3 children with autism develop seizures in childhood or
during adolescence, a serious problem considering that epilepsy,
in addition to immunological problems, more than doubles the
risk of early death in individuals with autism compared to healthy
population. One longitudinal study found that of the 120 individuals
with autism had died at the time of follow-up, a rate 5.6 times
higher than expected. Epilepsy has found to be a major negative
factors on cognitive, adaptive and behavioral/emotional outcomes
for individuals with autism. [18579647,
19838782,
17321709,
15946331,
18766162].

Gastrointestinal abnormalities in autism

Individuals with autistic spectrum disordesrs tend to suffer
from various, sometimes severe gastrointestinal problems. Children
with ASD are suspected to have a higher rate of gastrointestinal
(GI) symptoms when compared with children of either typical
development or another developmental disorder, although large-scale
studies are yet to be carried out and the significance of the
association between many gastrointestinal pathologies and autism
is yet to be confirmed.

A recent
concensus report on evaluation, diagnosis, and treatment of
gastrointestinal disorders in individuals with autism concluded
that care providers should be aware that problem behavior
in patients with ASDs may be the primary or sole symptom of
the underlying medical condition, including gastrointestinal
disorders, and guideliness have been issued on evaluation
and treatment of common gastrointestinal problems in children
with ASDs, such as abdominal pain, chronic constipation, and
gastroesophageal reflux disease (20048083,
20048084).

The most
frequent complaints are chronic constipation and/or
diarrhea (frequently accompanied by indigested or partially
digested food in stools), gaseousness, and abdominal discomfort
and distension [14523189].
Decreased sulfation capacity of the liver,
pathologic intestinal permeability, increased secretory response
to intravenous secretin injection, and decreased digestive enzyme
activities were reported in many children with autism. Treatment
of digestive problems is reported to have positive effects on
autistic behavior in some individuals [8888921,
12010627,
1176974].

Defects of innate immune responses in ASD children with GI problems
have been detected, and intestinal pathology,
including ileocolonic lymphoid nodular hyperplasia
(LNH) and mucosal inflammation, with enhanced
pro-inflammatory cytokine production, has been characterised
in varous studies. A majority of the children were shown to
have chronic swelling of the lymphoid tissue
lining the intestines, particularly near where the small and
large intestines meet, and chronic inflammation of the
large intestine. Secondary eosinophilic colitis has
also been observed in autism. There is a consistent profile
of CD3+ lymphocyte cytokines in the small and large intestinal
mucosa of these ASD children, involving increased pro-inflammatory
and decreased regulatory activities [16494951,
15741748,
11007230,
15622451,
20068312].
The mucosal immunopathology in children with autism is reported
to be suggestive of autoimmune lesion and is apparently distinct
from other inflammatory bowel diseases [11986981,
15031638]
(see also Immune/Inflammation).

One study examining histologic findings in children with autism
revealed high incidence of grade I or II reflux esophagitis,
chronic gastritis and chronic duodenitis.
The number of Paneth cells in the duodenal crypts was significantly
elevated in autistic children compared to controls. Low intestinal
carbohydrate digestive enzyme activity was
reported in over half of the children with autism, although
there was no abnormality found in pancreatic function. Seventy-five
percent of the autistic children had an increased pancreatico-biliary
fluid output after intravenous secretin administration, suggesting
an upregulation of secretin receptors in the
pancreas and liver [10547242].

There are also reports of prominent epithelium damage
[11241044],
and of significant alterations in the upper and lower intestinal
flora of children with autism. One striking finding
was complete absence of non-spore-forming anaerobes and microaerophilic
bacteria from control children and significant numbers of such
bacteria from children with autism. The faecal flora of ASD
patients was found to contain a higher incidence of the Clostridium
histolyticum group of bacteria than that of healthy children
[1552850,
12173102,
16157555].

On the other
hand a low-grade edotoxemia has recently been observed in autism.
Compared with healthy subjects, serum levels of bacterial endotoxin
were significantly higher in autistic patients and inversely
and independently correlated with the severity of autism symptoms,
noting the need for further studies to establish whether increased
endotoxin may contribute to the pathophysiology of inflammation
and behavioural and social impairments in autism (20097267).
Presence in blood of endotoxins produced by gastrointestinal
pathogens is indicative of impaired gastrointestinal permeability
and present in chronic infectious and inflammatory conditions
– a good example is the association of HIV-infection with
increased gut permeability and microbial translocation, evidenced
by increased circulating lipopolysaccharide (LPS) levels, mirroring
the above-mentioned findings in autism (17720995).

Neurotransmitter
abnormalities in autism

Abnormalities in neurotransmitter systems have frequently been
recorded in autism. Clinical observations include both elevated
and lowered levels of various neurotransmitters compared to
controls, including alterations in monoamine metabolism [3654486,
2653386, 3215884], neurotransmitter peptides [9018016, 9315980],
with considerably raised levels of beta-endorphin (for vasopressin/oxytocin
see Hormones) and altered activities of cholinergic receptors,
with binding of muscarinic M(1) receptor being up to 30% and
that of nicotinic receptors being 65%-73% lower in the autistic
group compared to controls [11431227]. Postmortem brain examination
noted abnormalities of the glutamate neurotransmitter system
in autism, with specific abnormalities in the AMPA-type glutamate
receptors and glutamate transporters in the cerebellum [11706102].

Dysregulations
of serotonergic systems in particular have been documented,
such as abnormalities in brain serotonin sythesis, with significant
reductions in synthesis capacity compared to controls [10072042,
9382481], while at the same time plasma levels of serotonin
and free thryptophan appear to be on average 30-50% percent
higher in individuals with autism [6204248]. Autoantibodies
to serotonin receptors [9067002] and reduced receptor binding
have also been recorded [16648340]. Of note is that one study
found correlation of elevated plasma serotonin levels and the
the major histocompatibility complex (MHC) types associated
with autism [8904735].

Relative
to expression and function of nicotinic receptors in autism,
significantly lowered binding of some agonists to nicotinic
receptors has been observed. For example binding of the agonist
epibatidine in cortical areas to was up to 73% lower in autism
group compared to controls. As with serotonine receptors, some
of the nicotinic receptors have been noted to be significantly
permeable to calcium and so able to regulate several neuronal
processes. Of interest are the preliminary reports of therapeutic
action of galantamine in autism [15152789, 17069550], considering
that neuroprotective actions of galantamine are thought to be
linked to its modulation of nicotinic receptors [12649296].

A postmortem
study revealed greatly reduced levels of glutamic acid decarboxylase
(GAD) 65 and 67 kDa proteins in several areas of the brains
of individuals with autism [12372652].This was confirmed by
more recent results that showing GAD67 mRNA level reduced by
40% in the autistic group when compared to controls [17235515].
Another study found serum levels of glutamate in the patients
with autism were significantly higher than those of normal controls
[16863675].

Hormonal
abnormalities in autism

Abnormalities in hormonal metabolism are frequently observed
in individuals with autism, with several studies observing abnormal
levels of many hormons and their receptors compared to healthy
controls, as well as abnormal hormonal secretion rhythms [2713159,
1904373, 12959423, 10808042].

For example
the analysis of the Hypothalamic-Pituitary-Adrenocortical (HPA)
system responses observed more variable circadian rhythm as
well as significant elevations in cortisol following exposure
to a novel stimulus in children with autism compared to controls.
This exaggerated cortisol response is indicative of dysfunction
of the HPA system in autism (16005570). Over-reaction of the
endocrine system to insulin stress in autism has been recorded
in another study, whereas the experimental stress of insulin-induced
hypoglycemia showed slower recovery of blood glucose, much faster
cortisol response and elevation of growth hormone levels compared
to controls (1176974, 2870051). Low levels of insulin-like growth
factor-I (IGF-I) in cerebrospinal fluid have also been observed
(16904022).

Metabolic
disorders of serotonin and dopamine systems have been suggested
in autism, with approximately thirty percent of individuals
with autism exhibiting high levels of serotonin, simultanous
with lowered levels of melatonin (see Neurotransmitters). Melatonin
is converted from serotonin by several enzymes of the pinealocytes
in the pineal gland, including 5-HT N-acetyl transferase and
5-hydroxyindole-O-methyltransferase. Results of the studies
looking at sleep disturbances in autism suggest that both dyssomnias
and parasomnias are very prevalent in the disorders - people
with autism frequently experience sleep disorders and exhibit
atypical sleep architecture (10722958, 15705609, 17001527).
Further evidence of dysfunction of pineal endocrine system in
autism was obtained by looking at alterations of the light and
dark circadian rhythm of melatonin, where none of autistic patient
showed a normal melatonin circadian rhythm, together with once
again significantly lower levels of this hormone (11455326).

Leptin
is a hormone linked to melatonin that plays an important role
in amongst other things regulation of appetite and metabolism.
Results from a recent study have demonstrated significant differences
in leptin concentrations between children with autism and controls
(17347881).

Individuals
with autism often present with auditory, visual, tactile and
oral sensory processing disorders, as well as various forms
of motor difficulties, including dyspraxia (occasionally linked
to low muscle tone), dystonia (involuntary, sustained muscle
contractions) and ataxia (16940314, 17016677, 15514415, 16903124,
12639336). Visual disturbances in autism often include abnormalities
of colour perception (16598434) and weak visual coherence. Retinal
dysfunction in autism has been suggested, as well as deficits
in visual processing in dorsal cortex (3341467, 15958508). Abnormal
pain perception is sometimes present in autism, as well as self-injurious
behaviour.

Dyspraxia
is a disorder of coordination that can also be described as
a difficulty with planning a sequence of coordinated movements,
or in the case of ideo-motor dyspraxia, a difficulty with executing
a known plan. Various areas of difficulty can include speech
and language, fine motor control (eg handwriting or holding
pencil in a correct way), poor spacial awareness and timing
and balance of body movements and difficulty combining movements,
poor physical play skills (throwing and catching a ball) and
difficulty in manipulating small objects. Ataxia refers more
specifically to a failure of muscle control in limbs, often
resulting in a lack of balance and coordination and abnormal
gait.

Reduced cerebral blood flow and cerebral edema in autism

Results
of several studies have shown abnormal platelet reactivity and
altered blood flow in children with autism. Following these
findings it has been suggested that platelet and vascular endothelium
activation could be one of the contributing factors to the development
and clinical manifestations of the disorder (16908745). Relative
to this the following case reports are of particular interest,
both describing cases of inflammation of brain blood vessels
resulting in loss of language and emergence of symptoms of autism.
In both cases administration of nicardipine lead to recovery
of language and behaviour (1373338, 11008286).
PET and SPECT scans in autistic children show a decreased cerebral
blood floow in some regions of the brain (12077922, 10960047,
7790938) and cerebral water content was found to be raised in
brain grey matter in children with autism (16924017). A model
has been suggested in which the observed gray matter abnormality
could be inflammatory (see Immunity-Inflammation section below).
This finding of celebral edema at the same time offered an alternative
explanation for enlarged brain size in autism, which up to then
had been hypothesised to be due to lack ‘pruning’
of neurons during development.

Abnormality of the immune function and chronic inflammation
in autism

Results
of numerous studies point to an abnormality of the immune function
in autism, as well as active, ongoing inflammation in the GI
tract, the brain and the cerebrospinal fluid (CSF).

A recent
study by Vargas et al (15546155) investigated the presence of
immune activation in postmortem brain specimens and CFS from
subjects with autism. The authors found active neuroinflammation
in multiple areas of the brain, for example in the cerebral
cortex and white matter, and in the cerebellum. A marked migroglial
and astroglial activation was also found, as well as the presence
of an altered cytokine pattern, with macrophage chemoattractant
protein (MCP)-1 and tumor growth factor-beta1 (TGF-beta1) being
the most prevalent cytokines. There was also an accumulation
of macrophages and monocytes, and a marked absence of lymphocytes
and antibodies, pointing toward an innate neuroimmune activation
with the absence of adaptive immune system/T cell activation
in the brain. In addition, an enhanced proinflammatory cytokine
profile was observed in the CSF, including once more a marked
increase in MCP-1. These observations resemble findings in other
neurological disorders in which elevations in cytokine levels
is associated with the pathogenesis of neuroinflammation, neurotoxicity
and neuronal injury and subsequent behavioural and cognitive
impairments, for example HIV-associated dementia and multiple
sclerosis (15288500, 11282546, 16875710, 9852582). Animal experiments
illustrate that, during early pre and postnatal development,
inflammatory cytokine challenge can induce various psychological,
behavioral and cognitive impairments (17804539, 16147952, 9852582).
At the same time the expression of many cytokines, including
MCP-1, in neurons and glial cells seems to be upregulated by
increased intracellular calcium triggered by membrane depolarisation
(11102468, 10943723).

Another
investigation into inflammatory markers in the brain tissue
of patients with autisms revealed significantly increased levels
of several proinflammatory cytokines (TNF-alpha, IL-6 and GM-CSF,
IFN-gamma, IL-8). The Th1/Th2 ratio was also significantly increased
in ASD patients, suggesting that localized brain inflammation
and autoimmune disorder may be involved in the pathogenesis
of ASD (19157572).

Various
serological findings further confirm the presence of immune
system dysregulation and active inflammation in autism - raised
levels of proinflammatory cytokines have often been observed
in blood of patients with autism, with significant increases
of IFN-gamma, IL-6 and TNF-alpha. These results are followed
by findings of decreased peripheral lymphocyte numbers, incomplete
or partial T cell activation following stimulation, decreased
NK cells activity, dysregulated apoptosis mechanisms, imbalances
of serum immunoglobulin levels, increased numbers of monocytes
and abnormal T helper cell (Th1/Th2) ratio, with a Th2 predominance,
and without the compensatory increase in the regulatory cytokine
IL-10 (16698940, 16360218). It is of interest to note that,
following increased levels of TGF-beta1 in brain specimen as
observed by Vargas et al, this cytokine was found to be significantly
lower in the blood of adult patients with autism compared to
controls (17030376).

Another
relevant observation is the elevation of cerebrospinal fluid
levels of TNF-alpha compared to its serum levels in subjects
with autism. The observed ratio of 53.7:1 is significantly higher
than the elevations reported for other pathological states for
which cerebrospinal fluid and serum tumor necrosis factor-alpha
levels have been simultaneously measured (17560496).

It has
been suggested that prenatal viral infection might dysregulate
fetal immune system, resulting in viral tolerance in autism
(139400). Studies showing altered T-cell subsets raised suspicions
about possibile autoimmune aspects of autism and several studies
pointed to association of the risk of autism to immune genes
located in the human leukocyte antigen (HLA) (16720216, 15694999).
The immune system uses the HLAs to differentiate self cells
and non-self cells and some of them are linked with higher risk
of autoimmune disorders. Animal studies show that behavioural
changes follow onset of autoimmune disease and can be reversed
through immune-suppressive treatments (8559794), and although
various autoantibodies to brain antigens have been observed
in autism, the results of those studies are often conflicting.
In addition to the inconsistent findings the question has been
raised as to whether those autoantibodies would be pathogenic
contributors or mere consequences of the the disorder. Of note
in this context is the finding pointing to possible association
of virus serology and brain autoantibodies in autism (9756729).
One study found that children with autism had a significantly
higher percent seropositivity of anti-nuclear antibodies. Anti-nuclear
antibody seropositivity was significantly higher in autistic
children with a family history of autoimmunity than those without
such history, and also had significant positive associations
with disease severity, mental retardation and electroencephalogram
abnormalities (19135624). Autistic children were found to have
significantly higher serum anti-myelin-associated glycoprotein
antibodies than healthy children. Family history of autoimmunity
in autistic children was significantly higher than controls.
Anti-myelin-associated glycoprotein serum levels were significantly
higher in autistic children with than those without such history
(19073846).

A study
looking at several markers of concomitant autoimmunity and immune
tolerance found highly elevated circulating IgA and IgG autoantibodies
to casein and gluten dietary proteins in autism sample compared
to controls. Circulating anti-measles, anti-mumps and anti-rubella
IgG were positive in only 50%, 73.3% and 53.3% of autistic children
previously immunised by MMR, as compared to 100% positivity
in the control group. Anti-cytomegalovirus CMV IgG was also
investigated and was positive in 43.3% of the autistic children
as compared to 7% in the control group (17974154).

A recent
study found polyomavirus infection in postmortem autistic brains
BKV, JCV, and SV40 viruses were significantly more frequent
among autistic patients compared to controls [20345322].
Also worth noting is the finding that a large subset of subjects
with autism shows evidence of bacterial and/or viral infections
not present in age-matched controls [17265454],
as well as a reduced response to vaccine antigens, especially
Bortedella pertussis [link]. In
additon, there appears to be a correlation between of virus
serology and brain autoantibodies in autism.

Oxidative stress in autism

Oxidative stress is defined as an imbalance between pro-oxidants
and anti-oxidants, resulting in damage to cell by reactive oxygen
species (ROS). During times of environmental stress ROS levels
can increase dramatically which can result in significant damage
to cell structures, especially in absence of anti-oxidant defences,
such as the enzymes superoxide dismutase, catalase, glutathione
peroxidase and glutathione reductase or antioxidant vitamins
A, C and E and polyphenol antioxidants. There is mounting evidence
that abnormalities of ROS and nitric oxide (NO) may underlie
a wide range of neuropsychiatric disorders. Abnormal methionine
metabolism, high levels of homocysteine and oxidative stress
are also generally associated with neuropsychiatric disorders.
NO signalling has been implicated in a number of physiological
functions such as noradrenaline and dopamine releases. It is
thought to have neuroprotective effects at low to moderate concentrations,
but excessive NO production can cause oxidative stress to neurons
thus impairing their function.

Studies
comparing the level of homocysteine and other biomarkers in
children with autism to controls showed that in children with
autism there were highter levels of homocysteine, which was
negatively correlated with glutathione peroxidase activity,
low human paraoxonase 1 arylesterase activity, suboptimal levels
of vitamin B 12 (16297937, 12445495) and increased levels of
NO (12691871, 14960298).

Lipid peroxidation
was found to be elevated in autism indicating increased oxidative
stress. Moderate to dramatic increases in isoprostane levels
(16081262, 16908745), decreased levels of phosphatidylethanolamine
and increased levels phosphatidylserine (16766163) were observed
in children with autism as compared to controls. Levels of major
antioxidant proteins transferrin (iron-binding protein) and
ceruloplasmin (copper-binding protein) were found to be significantly
reduced in sera of autistic children. A strong correlation was
observed between reduced levels of these proteins and loss of
previously acquired language skills (15363659).

Another
study measured levels of metabolites in methionine pathways
in autistic children and found that plasma methionine and the
ratio of S-adenosylmethionine (SAM) to S-adenosyl-homocysteine
(SAH), an indicator of methylation capacity, were significantly
decreased in the autistic children relative to controls. In
addition, plasma levels of cysteine, glutathione, and the ratio
of reduced to oxidized glutathione, indicative of antioxidant
capacity and redox homeostasis, were significantly decreased
in autistic group. The same study evaluated common polymorphic
variants known to modulate these metabolic pathways in 360 autistic
children and 205 controls. Differences in allele frequency and/or
significant gene-gene interactions were found for relevant genes
encoding the reduced folate carrier (RFC 80G), transcobalamin
II (TCN2 776G), catechol- O-methyltransferase (COMT 472G), methylenetetrahydrofolate
reductase (MTHFR 677C and 1298A), and glutathione-S-transferase
(GST M1) (16917939).

Oxidative
damage in autism is also associated with altered expression
of brain neurotrophins critical for normal brain growth and
differentiation. An increase in 3-nitrotyrosine (3-NT), a marker
of oxidative stress damage to proteins in autistic cerebella
has been reported. Altered levels of brain NT-3 are likely to
contribute to autistic pathology not only by affecting brain
axonal targeting and synapse formation but also by further exacerbating
oxidative stress and possibly contributing to Purkinje cell
abnormalities (19357934).

A study
looking into cellular and mitochondrial glutathione redox imbalance
in lymphoblastoid cells derived from children with autism found
that, compared to controls, autism LCLs exhibit a reduced glutathione
reserve capacity in both cytosol and mitochondria that may compromise
antioxidant defense and detoxification capacity under prooxidant
conditions (19307255).

Mitochondrial dysfunction in autism

Mitochondrial dysfunction with defects in oxidative phosphorylation
has been suspected in autism and several recent findings that
show abnormalities in mitochondrial enzyme activities that support
hypothesis. Postmortem examination of autistic brains revealed
significantly elevated calcium levels in autistic brains compared
to controls, followed by elevations of mitochondrial aspartate/glutamate
carrier rates and mitochondrial metabolism and oxydation rates
(18607376, also see Brain and Oxidative Stress sections above).

When compared
to controls autistic patients show significantly lower carnitine
levels, followed by elevated levels of lactate, aspartate aminotransferase,
creatine kinase and significantly elevated levels of alanine
and ammonia (16566887, 15739723, 15679182). A pilot study investigating
brain high energy phosphate and membrane phospholipid metabolism
in individuals with autism found decreased levels of phosphocreatine
and esterified ends (alpha ATP + alpha ADP + dinucleotides +
diphosphosugars) compared to the controls. When the metabolite
levels were compared with neuropsychologic and language test
scores, a common pattern of correlations was observed across
measures in the autistic group, wherein as test performance
declined, levels of high energy phosphate compounds and of membrane
building blocks decreased, and levels of membrane breakdown
products increased. The authors concluded that the results of
the study provided tentative evidence of alterations in brain
energy and phospholipid metabolism in autism that correlate
with the level of neuropsychologic and language deficits (8373914).
This was further confirmed by another study finding the impairment
of energy metabolism in autistic patients which could be correlated
to the oxidative stress (19376103).
Also see above section- Oxidative Stresswww.wiki4cam.org/